The research of this program concentrates on the structural aspects of the rod outer segment disk membrane of the bovine eye by means of X-ray diffraction. Knowledge of this structure is necessary for an understanding of how photon absorption leads to neural stimulation. Efforts to date have been subject to uncertainties because of the long time exposures required. Using the image intensification-computer controlled TV data acquisition and analysis techniques we have developed, we can obtain data in much shorter times than previously and analyze to determine the conformatioal changes upon bleaching, as well as some information about the orientation and extent of the protein in the disk. Our goals for the coming year include I) map out the full range of hydrations over which the disk specimen is stable; II) acquire hydrated-specimen, high resolution data; III) augment the interpretation of I) and II) with labeling studies; IV) acquire high resolution data on changes in the membrane profile on bleaching; V) examine non-lamellar featues of the X-ray diffraction patterns to study tertiary conformation of rhodopsin; VI) search for in-plane changes in the mobility of proteins in the membrane upon bleaching.